In an RFID system, an RFID reader may be required to communicate with a large number of different RFID tags within a given communication range. Where each of the different RFID tags is identified by a unique identification number, it is imperative that the RFID reader be able to quickly and accurately read the identification number associated with each tag.
Many RFID applications, such as warehouse or “dock door” applications, have multiple RFID readers deployed in close proximity to one another. In these densely packed environments, the multiple RFID readers may be attempting to read one or more tag populations simultaneously. Depending on the power and range of each reader, a reader has a high probability of interfering with the communication attempts of another reader. For example, tag readers that are operating at the same frequency may directly interfere with each other if the readers attempt to read tags simultaneously. This direct interference can be minimized through the use of frequency hopping techniques. However, a tag reader that is hopping or altering its carrier frequency periodically can still interfere with another tag reader operating in an adjacent channel through side band cancellation.
In addition, techniques for reducing interference are limited by regulatory and operational considerations associated with frequency and bandwidth. For example, for frequency hopping systems operating in the 902-928 MHz band, the Federal Communication Commission (FCC) limits the maximum bandwidth of hopping channels to 500 kHz. Therefore, any technique to further reduce interference in a frequency hopping system must not cause a reader to exceed this maximum bandwidth.
What is therefore needed is a method for further reducing interference in a multiple reader environment without exceeding the bandwidth of the channel of operation.